Threat to dikes is real, says Cumberland County's EMO co-ordinator

Graphic from an Atlantic Climate Adaptation Solutions Association study shows the maximum extent of a water level of eight metres which overtops at sections of all the dykes. Highway routes are labelled since the TCH and CNR would not be passible at this level. - Submitted

Probability of dikes being overtopped increases with time

AMHERST – Cumberland County’s emergency measures co-ordinator says fears regarding the conditions of dikes on the Tantramar Marsh between Amherst and Sackville, N.B. are more than idle talk.

“It’s a very real risk,” Mike Johnson said after speaking to members of the Amherst Rotary Club on Monday. “It’s a threat that’s only going to get more pronounced as we continue into the future.”

Johnson has been out on the marsh at times when the tides have been at their highest, including the 2015 King Tides when the water from the Bay of Fundy was lapping at the top of the dikes between the community – and in at least one case trickled over the top of the dike in Aulac, N.B.

He said there are a number of factors that require action sooner than later. It’s well known that sea levels are rising and with global warming there’s an increased risk of more severe storms. Those, combined with an astronomically high tide, every 18 years could lead to disaster if that high tide, or King Tide, occurred at a time when a major storm, such as a hurricane were coming up the bay.

“The risk is having a high tide at the same as an intense low pressure system that creates a storm surge,” Johnson said.

If a two-metre storm surge were to happen during a very high tide in the next few years, Johnson believes, at least 50 homes and businesses in the Amherst area would be at risk while Highway 2 (Lower LaPlanche Street) and the Trans-Canada Highway would be at risk of being compromised.

That risk could grow over time to also threaten the railway, causing millions of dollars in damage and lost trade. The other issue, he said, is once the water gets over the dike, it would be hard to get it out again and the cleanup could range from days to weeks for a minor event or months for a major one.

The potential for it happening soon is small, he admitted, but planning and preparations need to be done now for future generations.

“We really need to think about this now,” Johnson said. “We need to be prepared.”

For business and homeowners it means having a plan in place for what to do when they get the warning that a storm surge is coming.

“They have to be prepared to pick up their things and leave on short notice,” the EMO co-ordinator said. “They have to be prepared to go very quickly because there won’t be a lot of notice, so it’s best to have a plan in place now for when it does happen.”

Johnson’s concerns echo those of research scientist Tim Webster with the Applied Geomatics Research Group at the Nova Scotia Community College’s Middleton campus.

In 2009, he was hired by the province to study the flooding potential on the Isthmus of Chignecto in the Amherst area.

Using new elevation measurements of the land bridge connecting Nova Scotia and New Brunswick and factoring in predicted sea level rise, high tides, the fact the isthmus is sinking at a rate of 15 cm per century and a two-metre storm surge, he was able to map potential scenarios.

He said an eight-metre high tide and surge would come over top the dikes and put the Trans-Canada under water and make the railway impassible.

“There’s a relatively low probability of it happening, but if it does happen there will be severe consequences,” Webster said. “There’s a large tidal range in the Bay of Fundy so for a surge to go overtop the dikes it would have to happen at a high spring tide. That’s one thing that’s going for the area that lessens the probability of that happening.”

He suggests taking steps now, including either moving the highway and railway to higher ground (something he knows will require significant investment) or putting more money into the existing dikes to shore them up or make them higher.

Johnson’s comments come after Amherst Mayor David Kogon, Sackville, N.B. Mayor John Higham and Cumberland County Warden Allison Gillis met with Cumberland-Colchester MP Bill Casey and Beausejour MP Dominic LeBlanc to express their concern with the lack of work on upgrading the marsh.

The mayors and warden have also written infrastructure officials on both sides of the border asking for a meeting to discuss the process for making repairs to the dike infrastructure that dates back to the Acadian settlers of the late 1600s.